Society of Robots - Robot Forum

here's my archimedes pulley downgear system CAD for my 2430 bldc motor for finger actuation.  This will give 64:1 downgearing.  Compare this to 180:1 standard downgear ratio in a hobby mg996r servo motor for example.  Will be a bit faster than that then but still plenty of torque with this beefy bldc motor (200w motor).  I prefer pulleys over gears since they will operate mostly silently whereas gears are noisy.  I think this pulley system is the secret sauce of my plans that I am not aware anybody has done yet.  It could be the standard for humanoids one day maybe if it is as good as I think it will be.  Still experimental but I'm going to be prototyping this soon.  I will be making my own bearings for these pulleys so the whole pulley is custom made.  Well some pulleys I'll be using purchased mini ball bearings and some pulleys I'll be making the bearings as plain bearings using stainless steel tubing which I can cut to size with my dremel to make the plain bearing.  Another HUGE benefit of pulleys over gears is gears generally are mounted to top of motor which really makes a large volumetric area taken up by the motor and downgearing which creates space concerns for fitment inside tight spaces in humanoid form factor (particularly when you use a human bone structure instead of a hollow 3d printed arm with no bones which some have done to accomodate geared servos inside the hollowed arm space).  So by translating the motor's turning by way of braided PE fishing line to a pulley system like this, you can decouple the motor from the downgearing in your CAD design, placing the downgearing in a convenient place separate from the placement of the motor which allows for creative rearranging possiblities that enable you to cram way more motors and downgearing into the very limited spaces in the robot.  The motors and downgearing is fitting where muscles would normally be in a human body so you want elongated narrow fitment options and this way of downgearing lends to that shape requirement well.  Also it is nice not to have to worry about making or buying gears which can add cost and complexity and weight and a lot of volume concerns.  The noise elimination will be huge.

I'm planning to use .2mm 20lb test braided pe fishing line on the finger motors that will run to the pulley system and then swap to 70lb test line for some of the lower pulleys where the downgearing has beefed up the torque quite a bit and the tension will be higher there so going thicker line then.  70lb test will go to fingers from the final pulley of the archimedes pulley downgearing system. 

The 70lb test PE braided fishing line (hercules brand off Amazon) is .44 mm OD and pairs well with .56mm id ptfe teflon tube I can buy on ebay.  The 20lb test PE braided fishing line (hercules brand off Amazon) pairs well with 0.3mm id ptfe teflon tube.  The tube acts just like bike brakes line guidance hose to guide the string to its desired location.  Teflon is naturally very low friction.  I may also lube the string so the friction is even lower inside the tubing.  I'd use teflon lubricant for the lube.

I will be actively CAMPAIGNING AGAINST use of gears in robots because I think they are too loud and obnoxious.  BLDC motors are quiet and pulleys should be quiet too.  Having powerful, fast, and very quiet robots is ideal for home users who don't want a super loud power drill sound coming off their home robot.  I believe this downgearing by pulleys solves all of this and aught to be the way downgearing is done for humanoid robots as the standard approach going forward. - but of course someone has to be first to do it to prove it and show a way to approach this method and I seem to be the one for this task.  Note I can't recall but maybe there was one asian robotics team that used pulleys not sure.  I decided on pulleys before I came across that team but I'm fuzzy on that team's design now.  In any case, nobody to my knowledge has fully downgeared to 32:1 or 64:1 type ratios by way of pulleys before now so I'm definitely innovating that imo.

Note on low update frequency:  I work on the robot in spurts for like 3-4 weeks then go on to other projects for months at a time before coming back to the robot.  Lately I've been thinking I should do at least one tiny thing for the robot per day as a minimum to keep it in mind and keep progress less in spurts and more steady going.  This has been working well the past few months.  I'm making much more consistent progress and also life is getting more manageable with my babies now growing up into toddlers and lots of other competing projects getting sorted out and settled more and some done.  Can't wait till I can double or triple my time commitment to the robot.  It's hard to have the progress be so slow for me.  Especially since it's such a massive undertaking that the long breaks make getting started up again intimidating especially when you forget a lot of details of where you left off.

Note also that I did work a ton on the AI for the robot and have a lot of new videos on that stuff on my youtube channel going up lately.  That has been very fun and satisfying but I've only scratched the tip of the iceberg with that.  Maybe put in 80 hours of the required 10k+ hours to really get big results LOL. 

Note: I also have decided to make my own motor controllers from scratch to cut costs and have more control and less relying on a black box situation going on.  I want my microcontrollers to directly control and monitor ever detail of the rotation of the motors and report back to my main brains PC the status of things.  I designed the electronics for this with the help of electronoobs on youtube who did a series of videos on BLDC motor controllers of various types.  He helped me understand it alot and chatgpt answered tons of my questions and helped alot too.  I have 2 blueprints for my designs for these motor controllers which are done and also did 3d blueprints for them in CAD.  I also did a prototype which I still need to finish and test.  I also made a gerber file with intentions to have JLBPCB make some flexible small motor controller pcb parts for me but they were a total ripoff on price due to the complexity of my board and their pricing structure frowning on that.  So I'll be making my own circuitboards using diy methods instead going forward.  One more reason I decided to roll my own motor controller circuitboards is the huge space constraints I'm dealing with kind of forcing my hand to make my own circuits since commercial ones are not optimized for size enough to fit in the very tight constrained volumetric areas I have to work with.  So it was basically not even optional in my case.

Ideally if my designs work out, the motor controllers I make which will be super small and flexible on flat flex boards will become commercialized products one day and so will the archimedes pulley designs or at least mini pulleys themselves be able to be bought.  But since none of this stuff exists commercially I have to make it.  The price you pay to be a frontiersman and trend setter at the forefront of new technological areas of development.  All of these factors slow me down.

On a positive note I did find a time saver/shortcut.  I bought a lifesize humanoid doll that is fairly realistic looking to use as a outer shell for the robot.  It is a TPE doll.  I have to modify it to fit my PVC medical skeleton frame significantly so.  But it is easier than starting from scratch or 3d printing everything and making molds and casts and whatnot.  I plan to cut off its skin to make a sort of skin suit for the robot and also make my exoskeleton wireframe mesh that supports the skin using the modfied, skinned doll as a guide.

Does a cylindrical robot with 2 vertical rotary joints (one on base, one on arm) make it articulated?
If so, when I remove one rotary joint (base or arm), does that make it non articulated?
Thanks

At the present time, this is completely possible. I believe that in the future robots will become even more flexible.

I had these plans from American Robots in 1979 that would still hold up today!  I lost them.  They were for a 5 foot robot that resembled Robby The Robot, with working claws motors etc.  I lost them when I moved once and have been hunting for them ever since.  Going to be hard to recover something that old but here is hoping!

It's great that localities have so many competitions. I hope my product will be launched at a local exhibition soon.

Hej
Here is video of tracked robot
Aprox 90cm long, 100cm wide
Huge pulling power
3,5km/h speed

https://youtu.be/YxzEJLNGbfg?si=t1Ucj0dRnVzyrqaV

With headlight
https://youtu.be/bkoVwxcySC4?si=8KEQmbZMPL1HvyL8

Cutting big grass
https://youtu.be/zv21078iIw4


Thanks